Two types of suspension capable of providing the magnetic forces required for vehicle suspension are known in the art. They include:
1. Electromagnetic Suspension (EMS) wherein electromagnets on the vehicle are attracted to a guide-way which has ferromagnetic rails (Transrapid, Germany); and PA0 2. Electro-dynamic Suspension (EDS) wherein super-conductive magnets on the vehicle are repulsed from a guide-way which has nonmagnetic conductive rails (Japanese Maglev).
Both of these systems have serious drawbacks that delay their utilization for transportation needs.
EMS (Transrapid, Germany) fails to insure stable equilibrium of the vehicle without a fast-response automatic control system to control the size of the air gap between the electromagnet's poles and guide-way rails. Therefore, any failure in the control system or loss of current in the electromagnets may lead to a dangerous situation, and, possibly, to catastrophe. Moreover, the fast-response control system and also a large generator of current (with its own power supply) must be installed in the vehicle, so that the passenger/freight load comprises only a small fraction of the weight of the vehicle.
The EDS (Japanese Maglev) requires an on-board system for permanent cooling of super-conductive magnets. Failure to maintain the temperature strictly in pre-determined limits may lead to catastrophe. Moreover, although the super-conductive magnets produce a strong magnetic field, this field fails to provide sufficient forces for stable vehicle movement and, therefore, the EDS, similar to the EMS, also requires a fast-response control system and source of high power current to damp the vehicle vibration during turns. Besides, the strong magnetic field may be dangerous for passengers.
The other drawback of both systems is their low stiffness. It will be appreciated by those skilled in the art, that the coefficient of proportionality f.sub.s between the displacement and the increment of the internal stabilizing force is called "stiffness": EQU f.sub.s =.differential.F.sub.s /.differential..delta.
and represents the decisive parameter, i.e. the greater the stiffness, the smaller the displacement of the vehicle and, therefore, the better the quality of the magnetic suspension system.
Any suspension system functions by employing internal forces interacting between a magnetic field (produced by magnets located on the vehicle) and currents in guide-way rails (induced thereto by said magnetic field). As the distance from the magnets grows, the magnetic field subsides and the internal magnetic forces diminish, and their derivative--stiffness--diminishes at a more rapid (second-degree) rate.
The EMS system (Transrapid, Germany) never produces internal stabilizing forces. This system is internally unstable, and its stiffness is created and maintained artificially--by means of fast-response control system.
The poles of super-conductive magnets in the EDS system (Japanese Maglev) are covered with thick layers of thermo-insulation, and currents induced in the guide-way's rails are distributed over the layers' thickness. Accordingly, the distance between the magnets' poles and the induced currents in the rails is greater than the size of the air gap between the magnets' poles and the rails. Moreover, the value of the current induced in the non-magnetic conductive rail during the magnets' movement is many times smaller than in the magnetic steel rail. This tends to reduce the stabilizing internal magnetic force and the stiffness, which is much lower than is necessary for the stable movement.
According to Lagrangian theorem known to those skilled in the art (Pol Appell: Traite de Mecanique Rationnelle. Paris, Gauthier-Villars, Etc. Editeurs), if at a certain position of a conservative system, its potential energy has a strict local minimum, then that position is a stable equilibrium point of the system, in order to provide stable vehicle flight along an assigned trajectory, it is necessary and sufficient that the potential energy of such a system had a strict local minimum at all points of the trajectory.
Disadvantageously, the magnets of the existing systems do not have an equilibrium position therein, and the magnetic field is distributed in such a way as to create destabilizing forces only, tending to attract the magnets to the respective iron cores.
In order to provide stability to the existing systems, a fast-response automatic control system is necessary. Such control is expensive and unfortunately, is not reliable at present.
It would be highly desirable to provide a vehicle suspension free of the drawbacks of the existing systems (Transrapid, Germany and Japanese Maglev).
Different magnetic levitation self-regulating systems disclosed in U.S. Pat. Nos. 5,140,208; 5,218,257; and 5,319,275 (invented by the same inventor as the present invention), were proposed having enhanced stabilization forces designated for stable hovering of heavy bodies.
For example, U.S. Pat. No. 5,140,208 discloses a Self-Adjusting Magnetic Guidance System for Levitated Vehicle Guide-Way, which employs new magnetic devices comprising two C-shaped steel cores affixed on the guide-way and a group of permanent magnets (further referred to as PMs) affixed to the bottom of the vehicle. The magnetic flux threads the PMs and steel cores. Affixed to the guide-way, the steel cores stretch magnetic flux tubes exisiting in the air gap at the right and left sides of the PMs. At the shift of the PMs downwards by the weight of the vehicle, the magnetic flux tubes tend to shrink, and as a result, pull the PMs upwards to their equilibrium position by and engendered stabilizing force which is proportionate to the shift value. At any failure, the vehicle is maintained suspended within the magnetic field.
Disadvantageously, a lateral shift of the magnets engenders a substantial destabilizing force.
U.S. Pat. No. 5,218,257 discloses a Magnetic Levitation Self-Regulating System, consisting of magnetic devices identical to those described in the above patent. These magnetic devices are connected in such manner that the destabilizing force in each of them is compensated by the stabilizing force of an adjacent unit. Disadvantageously, the destabilizing forces in the system prevail the stabilizing forces, therefore, the full compensation is not achieved.
U.S. Pat. No. 5,319,275 discloses a Magnetic Levitation Self-Regulating System having enhanced stabilizing forces and solves the above problems by means of strip screens covering end faces of the cores and extended along the entire stator. However, in order to be effective, the screens should have considerable thickness (not less than 20% of the distance between the PMs in the unit), doubling the air gap between the PM and respective core, and thus substantially reducing the stabilizing force and the stiffness. This radically lowers the quality and increases the cost of the system.
It would be highly desirable to provide a magnetic levitation serf-regulating system overcoming the disadvantages of the above described systems.